The present invention relates to a field of a molding machine and, in particular, concerned to a system for feeding portions of material to a plastic-injection molding machine.
Several weight feeding apparatus and systems are known. These apparatus and systems are for feeding a large quantity of material. When a small quantity is needed, e.g., coloring material, in a producing system, volume methods are used to achieve the needed weight. Volume methods are used for feeding small quantities because of the difficulty of weighing a few grams in the production area, which is very noisy and shaky.
Volume feeding methods, which are used to achieve weight feeding, have some disadvantages. The specific gravity of a material can be changed e.g., in a new production batch, and therefore a new scaling is needed. The volume-weight scaling is a long process and requires skilled workers. Moreover, since the fed volume cannot be controlled the volume-feeding method assumes that the feeder dispenses equal portions permanently and therefore ignores the material streaming problems.
Feeding hopper usually has an outlet to feed the material. Part of the material, the material in the shaft that is perpendicular to the outlet, does not press on the hopper. This “outlet-shaft” causes an error in the hopper weighing since the material in the outlet-shaft or at least part of this material is not weighed. Load cells are calibrated when weighing such hoppers.
There is therefore a recognized need for, and it would be highly advantageous to have, a system for feeding portions of material to an injection-molding machine with the ability to accurately weigh feeding of small quantities of material.